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Abstract:

A burner for a flash smelting furnace. The burner includes a distributor
for receiving pulverous feed material from a plurality of feed pipes. The
distributor has at least one curved deflector that directs the feed
stream in an evenly distributed annulus into the sleeve of the burner.

Claims:

1. A burner for a flash smelting furnace, comprising: a burner block that
integrates with the roof of the furnace, the block having a nozzle
opening therethrough to communicate with the reaction shaft of the
furnace; a wind box to supply combustion gas to the reaction shaft
through the nozzle opening, the wind box being mounted over the nozzle;
an injector having a sleeve for delivering pulverous feed material to the
furnace and having a central lance within the sleeve to supply compressed
air for dispersing the pulverous feed material in the reaction shaft, the
injector mounting within the wind box so as to extend through the nozzle
opening in the block, defining therewith an annular channel through which
combustion gas from the wind box is supplied into the reaction shaft; and
a distributor for receiving pulverous feed material from a plurality of
feed pipes, the distributor having at least one curved deflector that
directs the feed stream in an evenly distributed annulus into the burner
sleeve.

2. The burner of claim 1 wherein the at least one curved deflector
comprises a plurality of deflector plates arranged in quadrants of the
distributor.

3. The burner of claim 1 wherein the at least one curved deflector
comprises a frustoconical skirt.

4. The burner of claim 1 wherein the distributor mounts at least
partially within the upper portion of the wind box.

5. The burner of claim 1 further comprising at least one inspection port
mounted to the wind box, the inspection port comprising a sight glass
with an internal guard movable from a first position protecting the sight
glass to a second position allowing viewing through the sight glass.

6. The burner of claim 5 wherein the internal guard is movable by means
of an external handle.

7. The burner of claim 6 wherein the internal guard is biased to rest
normally in the first position.

8. The burner of claim 1, wherein the wind box is dimensioned to have
sufficient volume to substantially slow down the incoming combustion gas
so that the pressure distribution is made effectively even.

9. The burner of claim 8, wherein the wind box is dimensioned to achieve
a reduction in velocity of the combustion gas of between 20% and 90% of
the inlet velocity.

10. The burner of claim 8, wherein the wind box has a generally biconical
shape.

11. The burner of claim 8, wherein the wind box has at least two
combustion gas inlets arranged radially symmetrically.

[0003] Flash smelting is a pyrometallurgical process in which a finely
ground feed material is combusted with a reaction gas. A flash smelting
furnace typically includes an elevated reaction shaft at the top of which
is positioned a burner where pulverous feed material and reaction gas are
brought together. In the case of copper smelting, the feed material is
typically ore concentrates containing both copper and iron sulfide
minerals. The concentrates are usually mixed with a silica flux and
combusted with pre-heated air or oxygen-enriched air. Molten droplets are
formed in the reaction shaft and fall to the hearth, forming a
copper-rich matte and an iron-rich slag layer. Much of the sulfur in the
concentrates combines with oxygen to produce sulfur dioxide which can be
exhausted from the furnace as a gas and further treated to produce
sulfuric acid.

[0004] A conventional burner for a flash smelter includes an injector
having a water-cooled sleeve and an internal central lance, a wind box,
and a cooling block that integrates with the roof of the furnace reaction
shaft. The lower portion of the injection sleeve and the inner edge of
the cooling block create an annular channel. The feed material is
introduced from above and descends through the injector sleeve into the
reaction shaft. Oxygen enriched combustion air enters the wind box and is
discharged to the reaction shaft through the annular channel. Deflection
of the feed material into the combustion air is promoted by a bell-shaped
tip at the lower end of the central lance. In addition, the tip includes
multiple perforation jets that direct compressed air outwardly to
disperse the feed material in an umbrella-shaped reaction zone. A
contoured adjustment ring is mounted slidingly around the lower portion
of the injector sleeve within the annular channel. The velocity of the
combustion air can be controlled to respond to different flow rates by
raising and lowering the adjustment ring with control rods that extend
upwardly through the wind box to increase or reduce the cross-sectional
flow area in the annular channel. Such a burner for a flash smelting
furnace is disclosed in U.S. Pat. No. 6,238,457.

[0005] Known burners of this type are associated with disadvantages that
can adversely affect their performance. These include failure to achieve
maximal mixing of the feed material with the combustion gas to optimize
oxygen efficiency within the reactor. In addition, such burners have
limited range of velocity control to optimize the performance of the
burner relative to the feed material. Known burners are also associated
with uneven distribution of feed material through the injector sleeve,
which can also adversely affect their performance.

[0006] For example, the control rods that raise and lower the adjustment
ring can interfere with the even flow of air through the wind box and
impede optimal mixing and combustion. It is also difficult to provide
water cooling for the adjustment ring, and the ring has a tendency to
become sticky or misaligned on the injector sleeve.

[0007] In addition, dispersion of feed material by compressed air is less
than optimal because the discreet jets used on known lance tips fail to
provide a continuous air curtain.

[0008] Moreover, known burner designs fail to include means for monitoring
how well centered the injector is within the annular channel, or
mechanisms for effectively adjusting the injector without having to shut
down the furnace.

[0009] It is a goal of the inventors to provide an improved burner and
burner feed apparatus for a flash smelting furnace that provides better
mixing, more optimal oxygen efficiency, improved control, and ease of
maintenance.

SUMMARY

[0010] The following summary is intended to introduce the reader to the
more detailed description that follows, and not to define or limit the
claimed subject matter.

[0011] According to one aspect, a burner is provided for a flash smelting
furnace. The burner includes a burner block, a wind box, an injector, and
an injector surrounding structure. The block integrates with the roof of
the furnace, and has an opening therethrough to communicate with the
reaction shaft of the furnace. The wind box is mounted over the block and
supplies combustion gas to the reaction shaft through the block opening.
The injector has a sleeve for delivering pulverous feed material to the
furnace and a central lance within the sleeve to supply compressed air
for dispersing the pulverous feed material in the reaction shaft. The
injector is mounted within the wind box so as to extend through the
opening in the block, defining therewith an annular channel through which
combustion air from the wind box is supplied into the reaction shaft. The
injector surrounding structure extends from the wind box through the
opening in the block. One of either the injector surrounding structure
and the injector is movable relative to the other by control means
exterior of the wind box so as to adjust the cross-sectional area of the
annular channel and thereby control the velocity of the combustion air
supplied into the reaction shaft.

[0012] In some examples the injector surrounding structure is a collar
movable by control means exterior of the wind box so as to adjust the
cross-sectional area of the annular channel and thereby control the
velocity of the combustion air supplied into the reaction shaft. The
collar may comprise a plurality of curved fins which pivot to expand or
contract the annular channel. Alternatively, the collar may comprise at
least one band which can be raised toward or lowered away from an
outwardly flared section on the sleeve to increase or reduce the annular
channel.

[0013] In other examples, the lower portion of the sleeve is upwardly
tapered and the injector surrounding structure has a generally
corresponding downward taper, and the injector can be raised and lowered
by control means exterior of the wind box so as to adjust the
cross-sectional area of the annular channel.

[0014] According to another aspect, a burner is provided for a flash
smelting furnace. The burner includes a burner block, a wind box, an
injector, and an injector surrounding structure. The block integrates
with the roof of the furnace, and has an opening therethrough to
communicate with the reaction shaft of the furnace. The wind box is
mounted over the block and supplies combustion gas to the reaction shaft
through the block opening. The injector has a sleeve for delivering
pulverous feed material to the furnace and a central lance within the
sleeve to supply compressed air for dispersing the pulverous feed
material in the reaction shaft. The injector is mounted within the wind
box so as to extend through the opening in the block, defining therewith
an annular channel through which combustion air from the wind box is
supplied into the reaction shaft. The upper portion of the sleeve of the
injector is mounted to the lower portion of the wind box with respective
flanges separated by a compression gasket and provided with leveling
adjusters.

[0015] According to another aspect, a burner is provided for a flash
smelting furnace. The burner includes a burner block, a wind box, an
injector, and an injector surrounding structure. The block integrates
with the roof of the furnace, and has an opening therethrough to
communicate with the reaction shaft of the furnace. The wind box is
mounted over the block and supplies combustion gas to the reaction shaft
through the block opening. The injector has a sleeve for delivering
pulverous feed material to the furnace and a central lance within the
sleeve to supply compressed air for dispersing the pulverous feed
material in the reaction shaft. The central lance includes an annular
slot at its tip for creating a substantially continuous air curtain.

[0016] According to another aspect, a burner feed apparatus is provided
for a flash smelting furnace. The burner feed apparatus includes a
distributor having curved deflector plates that direct the feed stream in
an evenly distributed annulus into the burner sleeve.

BRIEF DESCRIPTION OF DRAWINGS

[0017] In order that the claimed subject matter may be more fully
understood, reference will be made to the accompanying drawings, in
which:

[0018]FIG. 1 is an isometric view of a burner assembly and feed apparatus
for a flash smelting furnace according to one embodiment.

[0019]FIG. 2 is an enlarged isometric view of the burner assembly of FIG.
1.

[0020]FIG. 3 is a cross-sectional view of the burner assembly of FIG. 2
with the combustion air channel most open.

[0021]FIG. 4 is a cross-sectional view of the burner assembly of FIG. 2
with the combustion air channel most closed.

[0022]FIG. 5 is a more detailed cross-sectional view of the lower portion
of the burner of FIG. 3.

[0023] FIG. 6 is a more detailed cross-sectional view of the lower portion
of the burner of FIG. 4.

[0024]FIG. 7 is an isolated isometric view of a portion of the collar
assembly that opens and closes the combustion air channel in the burner
of FIGS. 3 and 5.

[0025]FIG. 8 is an isolated isometric view of a portion of the collar
assembly that opens and closes the combustion air channel in the burner
of FIGS. 4 and 6.

[0026]FIG. 9 is an isolated perspective view of a portion of the control
ring and support frame for the collar assembly of FIGS. 7 and 8.

[0027] FIG. 10 is an isolated cross-sectional view of the injector of the
burner of the previous figures.

[0028] FIG. 11a is a more detailed cross-sectional view of the tip of the
injector.

[0029]FIG. 11b is an exploded isometric view of the tip of the injector.

[0030] FIG. 11c is a similar isometric view of the tip of the injector,
with internal structures shown in dotted lines.

[0031]FIG. 12 is a more detailed cross-sectional view of the upper
portion of the injector.

[0032] FIG. 13 is a plan view of the upper portion of the injector.

[0033] FIG. 14 is an isolated isometric view of a splitter box of the feed
apparatus.

[0034] FIG. 15 is an isolated isometric view of a manifold connector of
the feed apparatus.

[0035] FIG. 16 is an isolated isometric view of the feed pipes of the feed
apparatus.

[0036]FIG. 17 is an isometric view of the distributor of the feed
apparatus.

[0037]FIG. 18 is an isometric view from below of the upper portion of the
distributor of FIG. 17, revealing the interior thereof.

[0038] FIG. 19 is a perspective view of a burner assembly according to a
second embodiment.

[0039]FIG. 20 is a cross-sectional view of the burner assembly of FIG. 19
with the combustion air channel most open.

[0040]FIG. 21 is a cross-sectional view of the burner assembly of FIG. 19
with the combustion air channel most closed.

[0041]FIG. 22 is a cross-sectional view of a burner assembly according to
a third embodiment with the combustion air channel most open.

[0042]FIG. 23 is a more detailed cross-sectional view of the lower
portion of the burner of FIG. 22.

[0043]FIG. 24 is a more detailed cross-sectional view of the lower
portion of the burner of FIG. 22 with the combustion air channel most
closed.

[0044]FIG. 25 is a perspective view of a burner assembly according to a
fourth embodiment.

[0045]FIG. 26 is a cross-sectional view of the lower portion of the
injector of the burner of FIG. 25.

[0046]FIG. 27 is a more detailed cross-sectional view of the connection
surrounding the injector of the burner of FIG. 25.

[0047]FIG. 28 is a cross-sectional view of the feed distributor of the
burner of FIG. 25.

[0048] FIG. 29a is a cross-sectional view of an inspection port of the
burner of FIG. 25, with both its internal guard and external cover in
their closed positions.

[0049]FIG. 29b is a cross-sectional view of the same inspection port with
its internal guard in its open position and its external cover in its
closed position.

[0050]FIG. 29c is a cross-sectional view of the same inspection port with
both its internal guard and external cover in their open positions.

DETAILED DESCRIPTION OF EMBODIMENTS

[0051] In the following description, specific details are set out to
provide examples of the claimed subject matter. However, the embodiments
described below are not intended to define or limit the claimed subject
matter. It will be apparent to those skilled in the art that many
variations of the specific embodiments may be possible within the scope
of the claimed subject matter.

[0052] As shown in FIGS. 1-4, a burner assembly 13 is positioned above the
reaction shaft of a flash smelting furnace. The base of the burner
assembly 13 is provided by a block 14 which integrates into the roof of
the reaction shaft of the furnace. A wind box 15 is mounted above the
block 14 and an injector 16 having a sleeve 17 and a central lance 18
extends through the wind box 15 and through a nozzle opening 19 in the
block 14. Above the wind box 15 is the material feed equipment,
comprising air slides 20, splitter boxes 21, manifold connectors 12, feed
pipes 22, and a distributor 23 which communicates with the sleeve 17 of
the injector 16. The central lance 18 of the injector 16 extends upwardly
beyond the sleeve 17 through the top of the distributor 23 to a lance
head section 24.

[0053] As seen in FIGS. 3 and 4, the burner assembly 13 rests on the
burner block 14 which provides the main seal between the reaction shaft
of the furnace and the burner assembly 13. The block 14 is water-cooled
and has multiple ports for access to burner components. The injector
sleeve 17 extends into the upper portion of the reaction shaft of the
furnace. The central lance 18 has a tip 25 at its lower end which extends
below the sleeve 17. The lower rim 26 of the sleeve 17 is inwardly
chamfered and the lance tip 25 has a frustoconical shape and together
they direct the feed material outwardly. The lance 18 carries compressed
air which is directed horizontally from the tip 25. The compressed air
further disperses the feed material in an umbrella pattern. The opening
19 of the block 14 and the sleeve 17 define an annular channel through
which the combustion air passes from the wind box 15 to the reaction
shaft.

[0054] The wind box 15 communicates with the reaction shaft through a
variable collar 28 within the annular channel 27. The collar 28 provides
a nozzle function so that the velocity of the enriched air can be
controlled to accommodate different flow rates. As shown in FIGS. 5-9,
the collar 28 comprises sixteen curved fins which pivot to expand or
contract around the lower portion of the injector sleeve 17. Eight inner
fins 29 are tapered and have outwardly extending control arms 30. Eight
outer fins 31 overlap with the eight inner fins 29. The inner and outer
fins 29,31 include brackets 46 that rest on a machined insert 47, which
is also water cooled, that is fit into the opening 19 of the burner block
14. The eight outer fins 31 are spring loaded to maintain a tight
relationship with the eight inner fins 29. The outer fin control arms 30
interact via roller pins 32 with angled slots 33 in a surrounding control
ring 34 so that as the control ring 34 is rotated, the outer ends of the
fin control arms 30 are raised or lowered, thereby pivoting the eight
inner fins 29. In this manner, the collar 28 effectively varies the
cross-sectional area of the annular channel 27 between the sleeve 17 and
the collar 28.

[0055] As best seen in FIG. 9, the control ring 34 is held in place by a
plurality of rollers 35 positioned on a circular support frame 36 such
that the rollers 35 bear on the outer face and the upper and lower edges
of the control ring 34. The rollers are journalled in pivot mounts 37 to
adjust their position. The control ring 34 can be rotated by means of a
worm gear 38 and motor 39. Alternatively, the control ring could be
rotated by means of a pivot arm assembly or chain and sprocket drive
using either hydraulic, pneumatic or electrical actuators.

[0056] As seen in FIGS. 5 and 6, the collar 28 includes an upper section
40 having a flange 41 that connects with a corresponding lower flange 42
at the lower rim 43 of the wind box 15. The upper section 40 of the
collar 28 connects to the inner and outer fins 29, 31 by means of
cooperating lugs 44. A steel tension hoop 45 covers the gap between the
upper ring and the fins.

[0057] Cover plates 48 are mounted to the control ring support frame 36 to
enclose the area. A compressed air inlet is provided to maintain a
positive pressure within the enclosure formed by the cover plates to
prevent either combustion air or furnace gases from escaping.

[0058] As shown in FIGS. 3 and 4, and 10-13, the upper end of the injector
sleeve 17 has flanges 50,51 for mounting the injector 16 to corresponding
flanges 52,53 on the wind box 15 and the distributor 23. The upper flange
52 of the wind box 15 and the lower flange 50 of the sleeve 17 are
separated by a compression gasket 54 and provided with three-point
leveling adjusters 55. This allows the injector 16 to be correctly
centered to provide equalized air flow through the annular channel 27
between the sleeve 17 and the collar 28. The adjusters 55 consist of
three studs welded to the wind box upper flange 52, provided with wing
nuts to allow easy adjustment without requiring additional tools.

[0059] In addition, as shown in FIGS. 5 and 6, rodding mechanisms 57 are
provided at three points on the lower portion of the wind box 14 to give
feedback of the alignment of the injector sleeve 17 relative to the
collar 28. The sleeve 17 is set during cold installation and the rodding
mechanisms 57 are each calibrated to the stroke distance to touch the
sleeve 17. The zero point can be checked periodically during furnace
campaigns and deviations can be corrected by means of the leveling
adjusters 55.

[0060] The wind box 15 is a generally biconical barrel shape and provided
with inspection ports 58 where the burner flame can be observed, and also
where the verticality of the injector 16 can be visually assessed. The
wind box 15 is provided with four beams 59 by which the burner assembly
13 is mounted to the support frame of the furnace. Two or more
symmetrically arranged inlets may be used to promote symmetric flow of
the combustion gas through the nozzle opening 19. The wind box 15 is
dimensioned to provide sufficient volume to substantially slow down the
incoming combustion gas so that the pressure distribution of the
combustion gas is made effectively uniform. A reduction in velocity of
between 20% and 90% of the inlet velocity has been found advantageous.
This promotes a more even flow through the nozzle. It also buffers out
variations in flow rates from multiple inlets. The interior of the wind
box 15 is smooth and the lower surface of the wind box 15 merges via a
smooth transition to the nozzle opening 19 to promote streamline flow.

[0061] Turning to FIGS. 10-13, the central lance 18 of the injector 16 and
the sleeve 17 both include internal water cooling. (The interior of the
sleeve 17 is not shown but it includes either a water cooling coil or a
shell design whereby the water flows down the inside of the shell and up
the outside or vice versa.) Cast in place monel tubing 68 provides
cooling for the lance tip 25. The lance 18 has small guide wings 60 to
keep it centered within the sleeve 17 and is mounted with spring washers
61 to maintain tension. An auxiliary fuel line 62 extends through the
lance 18 to a central outlet 63 at the bottom of the tip 25. Cooling
lines 64 for the lance 18 are clustered around the auxiliary fuel line
62. The compressed air carried through the lance 18 is discharged through
an annular discharge slot 65 that extends around the tip 25 to form an
effective continuous air curtain. Gussets 66 and a base ring 67 maintain
the gap at a constant cross-section so that the flow is not choked prior
to going through the slot 65. The dimension of the gap provided by the
slot 65 can be adjusted by replacing the base ring 67 with a thicker or
thinner base ring, or by adding shims.

[0062] Above the burner assembly 13 is the feed equipment. As seen in
FIGS. 14-18, pulverous feed material such as copper sulfide concentrates
is charged via air slides 20. Two air slides 20 are provided for
redundancy. The feed material passes from each air slide 20 through a
splitter box 21 that separates the charge into four equal portions. The
outlet of each splitter box 21 passes through a manifold connector 12
where feed pipes 22 are attached. Pairs of feed pipes 22 from each
splitter box 20 and manifold connector 12 are combined to provide four
charging streams to the feed distributor 23. Each stream of feed material
goes into one quadrant of the distributor 23. In each quadrant, the feed
stream is distributed evenly by means of a curved plate 11 that directs
the feed material evenly around the quadrant of the feed distributor. The
feed material then flows in an evenly distributed annulus into the sleeve
17 of the burner injector 16.

[0063] Turning to FIGS. 19-21, an alternate embodiment is shown. Similar
components are given like names, and like reference numbers followed by
the letter "a", and their description will not be repeated.

[0064] In this embodiment, the injector sleeve 17a is supported by three
mechanical screw actuators 71. The actuators 71 serve to adjust the
height of the sleeve 17a as well as to center the injector 16a. They
allow for precise raising and lowering of the sleeve 17a when they are
moved in unison, and they allow for centering of the injector 16a when
they are controlled separately. The centering can be automated by having
three feedback sensors that provide feedback of the relative height of
each of the actuators 71 to the controller. The sensors may be yo-yo type
sensors or other sensors such as optical sensors.

[0065] The wall of the lower portion of the injector sleeve 17a is
enlarged to present an upward taper to its outer surface, while the inner
surface of the insert 47a is tapered downwardly at a similar but
shallower angle. The annular channel 27a between the injector sleeve 17a
and the block insert 47a is in its most open position when the actuators
71 are fully extended. At this point, the sleeve 17a is at its highest
position and the cross-sectional area through which the combustion air
enters the reaction shaft is at its maximum. As the actuators 71 are
lowered, the sleeve 17a is also lowered, which gradually closes off the
cross-sectional area where the combustion air enters the reaction shaft.
When the actuators 71 are retracted, the sleeve 17a is at its lowest
position and the annular area through which the enriched air enters the
reaction shaft is at its minimum. In this way the cross-sectional area of
the annular channel 27a can be adjusted, which in turn adjusts the
velocity of the combustion air enters the reaction shaft.

[0066] As the injector sleeve 17a moves, the injector 16a and the
distributor 23a move as well. The feed pipes 22a, however, do not move.
The linear motion is accommodated through the use of four expansion
joints 72 attached to the inlets of the charge distributor 23a and the
outlets of the feed pipes 22a.

[0067] Turning to FIGS. 22-24, a third embodiment is shown. Similar
components are given like names, and like reference numbers followed by
the letter "b", and their description will not be repeated.

[0068] In this embodiment, the lower portion of the sleeve 17b has a bell
shape with a downwardly flared section 81 terminating in a generally
straight lower rim section 82. A generally straight and cylindrical outer
collar 80 extends from the block 14b to the wind box 15b. Within the
outer collar 80 are mounted a plurality of sliding bands 83. The sliding
bands are raised and lowered by actuators (not shown) that are exterior
to the insert 47b and exterior to the wind box 15.

[0069] The annular channel 27b between the injector sleeve 17b and the
block insert 47b is in its most open position when the sliding bands are
fully raised. At this point, the cross-sectional area through which the
combustion air enters the reaction shaft is at its maximum. As the
sliding bands are lowered, the cross-sectional area where the combustion
air enters the reaction shaft is reduced. When the sliding bands are at
their lowest position the annular area through which the enriched air
enters the reaction shaft is at its minimum. In this way the
cross-sectional area of the annular channel 27b can be adjusted, which in
turn adjusts the velocity of the combustion air enters the reaction
shaft.

[0070] Turning to FIGS. 25-29c, a further embodiment is shown. Similar
components are given like names, and like reference numbers followed by
the letter "c", and their description will not be repeated.

[0071] In this embodiment, the burner block 84 is a fabricated steel and
stainless steel double walled construction with water cooling. The wind
box 15c connects to the block 84 with a tapered connection 87 that
surrounds the lower portion of the injector 16c

[0072] The distributor 23c mounts lower, partially within the wind box
15c, to reduce the overall height of the burner. The distributor 23c has
no quadrant partitions and instead of curved plates, the feed material is
deflected evenly around the injector sleeve 17c with a frustoconical
skirt 86. The wind box 15c connects with the block 84 through the tapered
connection 87. The injector sleeve 17c is enlarged at its lower portion
to present an upward taper to its outer surface. The inner surface of the
connection 87 is similarly tapered but at a shallower angle. The annular
channel 27c between the injector sleeve 17c and the connection 87 is
adjusted by raising and lowering the injector sleeve 17c by means of
actuators 71c. Fins 85 within the connection 87 help to maintain the
concentricity and verticality of the injector 16c. The fins 85 also aid
in reducing turbulence of the airflow. The connection 87 may be made of a
ceramic material, or may be coated with ceramic or other refractory to
protect it from the heat of the reaction shaft.

[0073] Turning to FIGS. 29a, 29b and 29c, each of the inspection ports 58c
includes a cylindrical casing 90 having a hinged cover 91 that holds the
sight glass 92. The hinged cover can be locked in place by means of a
latch 93, or can be opened, for example, to allow operators to take
measurements. The latch 91 includes a screw mechanism which can be used
to ensure that the cover is closed tightly, so as to compress a gasket
between it and the casing 90 to create a seal. An interior guard 94
protects the inside of the sight glass 92. The guard 94 can pivot by
means of a handle 95. The handle 95 is heavier than the guard 94 and is
oriented so that the force of gravity acting on the handle 95 will bias
the guard 94 to its closed position. When an operator wishes to view
inside the burner, the operator pulls up on the handle 95 which rotates
the guard 94 downwardly and out of the way.

[0074] It will be appreciated by those skilled in the art that many
variations are possible within the scope of the claimed subject matter.
The embodiments that have been described above are intended to be
illustrative and not defining or limiting. For example, the collar of the
third embodiment could be a single piece that can be moved up and down to
increase or decrease the cross-sectional area of the annular channel and
thereby control the velocity of the combustion air entering the reaction
shaft. In addition, the tip of the lance could be provided with
additional compressed air ports to aid in fluidizing the descending feed
material above the air curtain.